1. Field of the Invention
The present invention relates to an image forming apparatus which is so configured as to be capable of performing a double-sided printing to a sheet.
2. Description of the Related Art
For example, as disclosed in Japanese Patent No. 3440652, there has been a known sheet-reversing apparatus which is provided in an image forming apparatus and so configured as to be capable of performing a double-sided printing to a sheet. The sheet-reversing apparatus includes a pair of feed-in rollers for feeding the sheet into a reversing section, a pair of reversing rollers provided in the reversing section and capable of reversing a rotational direction, and a pair of feed-out rollers for feeding out a sheet which is reversed front and back, so that a conveying direction of a sheet, to which one-side printing is performed in an image forming section, is reversed by a switch-back method.
According to the image forming apparatus provided with the sheet-reversing apparatus, the sheet bearing a fixed toner image on one side is fed into the reversing section by a normal rotation of the feed-in roller and the reversing roller. After that, the sheet is pulled out of the reversing section by a reverse rotation of the reversing roller and fed out by the feed-out roller toward the image forming section again in a state of being reversed front and back, and then a processing of transferring a toner image performed with respect to a back side of the sheet. The sheet, whose back side having been subjected to the transferring processing, passes through the fixing section again, so that a fixing processing is applied to the sheet again. After that, the sheet is discharged to outside as a sheet having been subjected to the double-sided printing.
Usually, in such sheet-reversing apparatus, if a preceding sheet is not completely pulled out of the reversing section by the driving of the feed-out roller through the pair of reversing rollers, the next sheet cannot be fed into the reversing section, so that a lowering of efficiency in a processing may occur disadvantageously. For the purpose of dealing with such disadvantage, in the sheet-reversing apparatus disclosed in Japanese Patent No. 3440652, one of the pair of reversing roller is separated apart from the other one by driving of a solenoid at a timing when the sheet which is fed into the reversing section temporarily and thereafter pulled out from the reversing section by a reverse rotation of the reversing roller is nipped by the pair of feed-out rollers.
Accordingly, in a state where the pair of feed-out rollers nip the sheet, the sheet can be pulled out from the reversing section only by the driving of the feed-out rollers without especially using the reversing roller. Further, a clearance formed between the pair of reversing rollers enables an operation of feeding the next sheet to the reversing section through the clearance to be performed concurrently with the operation of pulling out the preceding sheet. At this time, the preceding sheet and the next sheet are temporarily present at the same time in the reversing section. Consequently, efficiency in processing a sheet can be improved.
However, using a solenoid to separate one of the pair of reversing rollers apart from the other one causes the number of parts to increase, so that the cost of the apparatus also increase.
Further, a solenoid is not good in response. Thus, in such a case where an operation is not performed appropriately but in delay when one reversing roller should be separated apart from the other reversing roller, a problem may arise in which the next sheet fed into the reversing section may collide with the reversing roller so that a jam may occur.